英和和英

名詞

sand jack (複数形 sand jacks)

1. (construction) A type of jack from which sand can be released gradually in small quantities when lowering something into position.
   • 1950 October, “Completion of Flood-Damage Repairs, East Coast Main Line”, in Railway Magazine, page 708:

     After being rolled into position, the span had to be lowered about 4 in. on to its bearings. This was accomplished by means of sand-jacks—a simple arrangement of piston and cylinder—by which movements to very fine limits are obtained by the controlled release of sand from an opening in the base of the cylinder.